Presently, conditions such as diabetic retinopathy and age-related macular degeneration are subject to photocoagulative treatment with visible laser light. While this type of visible laser light treatment halts the progress of the underlying disease, it can be problematic. For example, because the treatment entails exposing the eye to visible laser light for a long period of time (typically on the order of 100 ms), damage can be caused to the patient's sensory retina from the heat that is generated. During the treatment, heat is generated predominantly in the retinal pigmented epithelium (RPE), which is the melanin containing layer of the retina directly beneath the photoreceptors of the sensory retina. Although light is absorbed in the RPE, this type of treatment irreversibly damages the overlying sensory retina and negatively affects the patient's vision.
Another problem is that some treatments require the application of a large number of laser doses to the retina, which can be tedious and time consuming. Such treatments call for the application of each dose in the form of a laser beam spot applied to the target tissue for a predetermined amount of time. The physician is responsible for ensuring that each laser beam spot is properly positioned away from sensitive areas of the eye that could result in permanent damage. Since some treatments can require hundreds of laser beam spots to evenly treat the target tissue, the overall treatment time can be quite long and require great physician skill to ensure an even and adequate treatment of the entire target tissue area.
To reduce the treatment time needed for retinal photocoagulation, a system and method has been proposed for applying multiple laser spots automatically in the form of a pattern of spots, so that an area of target tissue is efficiently treated by multiple spots pre-positioned on the tissue in the form of the pattern. See for example U.S. Patent Publication US2006/0100677. However, rapid delivery of multiple beam spots in patterns raises new issues. For example, localized heating can occur with the rapid and consecutive delivery of adjacent beam spots within a pattern. Moreover, variations in the patterns are needed to provide better exclusion zone and beam spot density control (both for even density and variable density), as well as better system control through a graphic user interface.